62 research outputs found
On Multistage Learning a Hidden Hypergraph
Learning a hidden hypergraph is a natural generalization of the classical
group testing problem that consists in detecting unknown hypergraph
by carrying out edge-detecting tests. In the given paper we
focus our attention only on a specific family of localized
hypergraphs for which the total number of vertices , the number of
edges , , and the cardinality of any edge ,
. Our goal is to identify all edges of by
using the minimal number of tests. We develop an adaptive algorithm that
matches the information theory bound, i.e., the total number of tests of the
algorithm in the worst case is at most . We also discuss
a probabilistic generalization of the problem.Comment: 5 pages, IEEE conferenc
Magnetization Losses in Multiply Connected YBa2Cu3O6+x Coated Conductors
We report the results of a magnetization losses study in experimental
multifilament, multiply connected coated superconductors exposed to
time-varying magnetic field. In these samples, the superconducting layer is
divided into parallel stripes segregated by non-superconducting grooves. In
order to facilitate the current sharing between the stripes and thus increase
the reliability of the striated conductors, a sparse network of superconducting
bridges is superimposed on the striated film. We find that the presence of the
bridges does not substantially increase the magnetization losses, both
hysteresis and coupling, as long as the number of bridges per length of the
sample is not large. These results indicate that it is possible to find a
reasonable compromise between the competing requirements of connectivity and
loss reduction in an ac-tolerant version of the high temperature coated
conductors specifically designed for ac power applications.Comment: 19 pages, 12 figures to be published in J. Appl. Phy
Magneto-optical studies of the uniform critical state in bulk MgB2
We present a detailed magneto-optical investigation of the magnetic flux
penetration in polycrystalline MgB2 slabs made by direct reaction of B and Mg.
Our results unambiguously indicate a uniform, Bean critical state magnetization
behavior with almost no electromagnetic granularity. From the measured magnetic
flux profiles we were able to extract the temperature dependence of the
critical current density Jc(T). The Jc(T) value reaches 1.8x10^5 A/cm2 at 10K
and 0.12T, in good agreement with global magnetization measurements
Influence of vortex-vortex interaction on critical currents across low-angle grain boundaries in YBa2Cu3O7-delta thin films
Low-angle grain boundaries with misorientation angles theta < 5 degrees in
optimally doped thin films of YBCO are investigated by magnetooptical imaging.
By using a numerical inversion scheme of Biot-Savart's law the critical current
density across the grain boundary can be determined with a spatial resolution
of about 5 micrometers. Detailed investigation of the spatially resolved flux
density and current density data shows that the current density across the
boundary varies with varying local flux density. Combining the corresponding
flux and current pattern it is found that there exists a universal dependency
of the grain boundary current on the local flux density. A change in the local
flux density means a variation in the flux line-flux line distance. With this
knowledge a model is developped that explains the flux-current relation by
means of magnetic vortex-vortex interaction.Comment: 7 pages, 14 figure
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